def complement(seq): complement = {'A': 'T', 'C': 'G', 'G': 'C', 'T': 'A'} bases = list(seq) for i in range(len(bases)): bases[i] = complement[bases[i]] if complement.has_key(bases[i]) else bases[i] return ''.join(bases) def reverse_complement(seq): return complement(seq[::-1])